The present invention relates to a dynamic vibration absorber capable of suppressing vibrations in horizontal two-dimensional directions of a target or object structure.
Generally, a dynamic vibration absorber includes an additional weight portion which is subjected to a force of inertia by vibrations, a rigidity element for generating a reaction force to the inertia force applied to the additional weight portion and a damping element for absorbing vibration energy.
A conventional dynamic vibration absorber is constructed such that vibrations in a specified direction of an object structure are suppressed by vibrating an additional weight portion. Hence, if there are a plurality of directions in which vibrations are to be controlled, the vibration controlling equipment must contain the same number of dynamic vibration absorbers as that of directions of vibrations.
One example of the conventional dynamic vibration absorber will be described with reference to FIGS. 28A and 28B.
In FIGS. 28A and 28B, an object structure 301 to be damped placed on a floor 300 has two vibration directions of the x- and y- axis. On the object structure 301 are placed two dynamic vibration absorbers 302 corresponding to the directions of the vibrations. Each of the dynamic vibration absorbers 302 is locked to a locking structure 305. In each of the dynamic vibration absorbers, an additional weight portion 302a is supported by both a rigidity element 303 and a damping element 304.
In each of the dynamic vibration absorbers 302, when vibrations are generated in the object structure 301, the damping elements 304 reduce vibration energy while the rigidity elements 303 apply reaction forces to the force of inertial generated in the additional weight portions 302a. Thus, the dynamic vibration absorbers 302 provide the damping effect for the vibrations in the x- and y-axis directions, respectively. In other words, in the conventional dynamic vibration absorbers, the single dynamic vibration absorber is provided to surpress vibration in one direction, that is, one for the horizontal direction and the other for the vertical direction as in FIG. 28B.
In the conventional dynamic vibration absorbers of the structure described above, there is no problem in a case where there is a large space for installation of the dynamic vibration absorbers and a plurality of dynamic vibration absorbers can be hence provided in a large object structure, such as a building. However, where there is a limitation to the installation space for the dynamic vibration absorbers and where damping in a plurality of directions is required, as in a machinery, it is difficult to adequately install the vibration controlling devices having a conventional structure in which the directions of a vibrations of the additional weight portions are determined.